Photomechanical Deformation of Azobenzene-Functionalized Polyimides Synthesized with Bulky Substituents

Abstract

Photomechanical effects realized in azobenzene-functionalized polyimides have shown large deformation and an exceptional increase in photogenerated force output. Here, we synthesize and characterize the photomechanical output of a series of linear polyimide materials prepared with a bulky substituent, incorporated via the development of a new bis­(azobenzene-diamine) monomer containing a 9,9-diphenylfluorene cardo structure (azoCBODA). All six azoCBODA-containing polyimides are amorphous and exhibit high glass transition temperatures (T g) ranging from 298 to 358 °C, storage moduli ranging from 2.27 to 3.81 GPa (at 30 °C), and good thermal stability. The magnitude of the photoinduced mechanical response of the azobenzene-functionalized polyimide is correlated to the rotational freedom of the polyimide chains (resulting in extensive segmental mobility) and fractional free volume (FFV > 0.1).

Kinetics of Ordering and Deformation in Photosensitive Azobenzene LC Networks

“…The bending of the film is caused by attenuation of visible light across the film thickness due to a strong absorption by azobenzene moieties. Interestingly, even azobenzene-functionalized polyimides with high modulus, ~3 GPa, demonstrate large photoinduced bending induced by linearly polarized blue light of moderate intensity [ 26 , 27 ]. For a recent review on photomechanical effects in LC materials see the relevant contributions in [ 28 ].…”

Light‐Responsive Shape‐Changing Polymers

“…The effects of azobenzene concentration, crystallinity, free volume, prestretching, backbone rigidity, and light polarization on the bidirectional bending of azobenzene‐polyimide films were thoroughly scrutinized. A number of polymer backbone compositions exhibiting various magnitudes of bending angles and photogenerated stresses were created …”

Reprocessable Photodeformable Azobenzene Polymers

“…Although they could exhibit good photomechanical and mechanical properties, they have some obvious drawbacks such as the typical complicated crosslinking processes, low flexibility in fabrication, and less freedom for further processing and recycling. To address these issues, a number of reprocessable photodeformable azo polymers have been developed on the basis of different design strategies [ 29 , 31 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 ,…”

“…They can be mainly classified into two types, i.e., the physically crosslinked ones with dynamic non-covalent bond-involved networks [ 29 , 31 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ] and chemically crosslinked ones with dynamic covalent bond (DCB)-involved networks [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ]. In addition, some uncrosslinked photodeformable azo polymers have also been reported and constitute one special type of reprocessable photodeformable azo polymers, whose photodeformation behaviors are mainly induced by the selective reorientation of the azo moieties (become perpendicular to the polarization direction of the polarized light) under the irradiation of either polarized blue light [ 72 , 73 , 74 , 75 , 76 , 77 ] or interfering polarized light [ ...…”